VSASL Microvascular Pulsatility Mapping With Cardiac Gating
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Solution Overview
Problem
Existing MRI techniques are inadequate for measuring microvascular pulsatility, which is linked to cerebral microvasculature damage and cognitive disorders, and are limited by the small size and slow flow of microvascular vessels, especially at lower field strengths common in clinical scanners.
Innovation Solution
A cerebral perfusion technique called velocity-selective arterial spin labeling (VSASL) is used to measure microvascular pulsatility on clinical 3T scanners, employing a sequence design with a first and second velocity-selective pulse sequence to define the leading and trailing edges of a blood bolus, and retrospective cardiac gating to assess blood flow pulsatility in the microvasculature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MRI techniques (ASL or phase contrast) are used to measure blood flow, then arterial blood flow pulsatility can be measured, but microvascular pulsatility cannot be measured due to small vessel size and slow flow
Solution Approach 1:
The patent changes the measurement parameters by using velocity-selective labeling with specific cutoff velocities (e.g., 0.5 cm/s to 2 cm/s) to selectively label slow-flowing microvascular blood. This parameter adjustment enables detection of microvascular pulsatility that conventional techniques miss, resolving the contradiction between measurement precision and detection difficulty
Solution Approach 2:
The patent introduces VSASL as an intermediary technique between conventional ASL and direct microvascular observation. By using velocity-selective preparation pulses as a mediator, the system can indirectly measure microvascular pulsatility through labeled blood that has slowed in the microcirculation, overcoming the direct detection limitations
2Measurement precision
If velocity-selective pulse sequences are applied to define blood bolus edges, then microvascular flow can be tracked, but measurement complexity increases
Solution Approach 1:
The patent segments the blood bolus measurement into distinct components by applying separate velocity-selective pulses to mark the leading edge and trailing edge. This segmentation allows precise tracking of bolus boundaries and calculation of pulsatility indices, resolving the contradiction between measurement precision and device complexity through structured decomposition of the measurement process
3Measurement precision
If retrospective cardiac gating is used to assess pulsatility over cardiac cycle, then pulsatility index can be calculated, but data acquisition time increases
Solution Approach 1:
The patent performs preliminary velocity-selective labeling of the blood bolus before the cardiac cycle completes, then uses retrospective gating to sort the already-acquired data by cardiac phase. This preliminary action allows accurate pulsatility indexing without requiring additional real-time synchronization hardware, resolving the contradiction between measurement precision and acquisition time
Data Source
AI summary
Measuring microvascular pulsatility using velocity-selective ASL. An example method includes: magnetically labelling blood flow in a target area of a subject using a velocity-selective arterial spin labeling (VSASL) technique with a cutoff velocity by performing operations including: applying a first velocity-selective (VS) pulse sequence with the cutoff velocity to mark a leading edge of a blood bolus; and applying a second VS pulse sequence with the cutoff velocity to mark a trailing edge of the blood bolus; acquiring VSASL signals of the blood bolus for voxels corresponding to the target area; for each of the voxels, obtaining signal intensity information over a cardiac cycle by performing retroactive cardiac gating on the acquired VSASL signals corresponding to the voxel; and determining a pulsatility index for the voxel based on the signal intensity information; and generating a voxel-wise pulsatility index map for the target area using the pulsatility indexes of the voxels.